Original paper
Crystal structures of monoclinic variants of two SFCA structure-types containing significant Fe2+: crystal structure of monoclinic SFCA-II, Ca2.6 Fe3+ 8.0Fe2+ 3.4Al4O24; and proposed crystal structure of monoclinic SFCA-I, ideally, Ca 2Fe2+ 8Fe3+ 8Al4O28
Mumme, William G.; Gable, Robert W.
Neues Jahrbuch für Mineralogie - Abhandlungen Band 195 Heft 2 (2018), p. 89 - 100
published: Aug 1, 2018
ArtNo. ESP154019502000, Price: 29.00 €
Abstract
Determination of the crystal structure of a new calcium alumoferrite has proved it to be a monoclinic variant of the previously determined SFCA-type, triclinic SFCA-II. It has formed during firing mixtures of ternary phase compositions in the CaO-Fe2 O3-Al2 O3 system (CF2 A) under reducing conditions. Monoclinic SFCA-II has the cell dimensions a = 10.335, b = 17.987, c = 10.488 Å, β = 109.50°, V = 1838 Å3, Z = 8, and space group symmetry P2/n. Its composition, determined from the crystal structure refinement, is Ca1.2 Fe 3+ 4.0Fe 2+ 1.8Al2O12, (M9O12). Monoclinic SFCA-II is a disordered structure composed of polysomatic sequences of pyroxene (P) and spinel (S) modules and, in this context, may be represented by the polysomatic formulation . Further, a crystal structure for a monoclinic variant of triclinic SFCA-I is proposed. The unit cell dimensions of this phase are a = 10.34, b = 21.44, c = 10.50 Å, β = 109.96°, P21/nsymmetry. The ideal composition of this phase is Ca 2Fe2+ 8Fe3+ 8Al4O28, (M11O14). In this case the structure may be represented by the polysomatic formulation of pyroxene (P) and spinel (S) modules as .
Keywords
crystal structure • polysomatism • monoclinic variants of sfca-types • silico-ferrites of calcium and aluminium